92 



COMPARATIVE ANATOMY 



The columella here also probably arises in connection with the upper end 

 of the hyoid arch (see p. 84), with which it is continuous in Hatteria. 



The quadrate alone forms as the suspensorium for the lower 

 jaw : it may be articulated with the skull (Ophidia, 1 most 



. Lacertilia) or firmly fixed to it 

 JC x^X^Hatteria, Chelonia, Crocodilia). 



According to Gaupp, a squamosal is 

 wanting in narrow-mouthed Snakes and 

 Hatteria, and a paraqiiadrate, comparable 

 to^tnat of the Amphibia (p. 85) is present 

 in almost all Lizards and Chelonians, a 

 quadratojugal being found only in Hatteria. 



The pterygopalatine arch is well 

 developed in all Reptiles. In Snakes 

 and Lizards it is more or less movable 

 and free from the base of the skull, 

 while in Chelonians and Crocodiles it 

 meets with its fellow to a greater or 

 less extent in the middle line, and 

 shelf-like palatine processes of the 

 maxilla also come into connection 

 with the palatines : thus a secondary 

 roof is formed to the mouth- cavity 

 distinct from the true (sphenoidal) 

 base of the skull. The cavity thus 

 formed closes in the posterior pro- 

 longation of the nasal chambers, 

 which consequently become sharply 

 differentiated from the mouth. In 

 Chelonians the pterygoid bones do 

 not take part in the formation of this 

 hard palate, which in Crocodiles is 

 much more markedly developed, 

 and is formed by the premaxillas, 

 maxillae, palatines, and pterygoids, 

 the posterior nostrils here opening 

 far back into the pharynx (Fig. 75). 



A number of bones arise in connection with the lower jaw, 

 viz., a dentary, angular, supra-angular, splenial, coronoid, and 

 articular. 



Teeth are well developed in all Reptiles except Chelonians, 



1 In Snakes (Figs. 72 and 73) (except Tortrix), the quadrate is only indirectly 

 connected with the skull by means of the squamosal, which extends backwards, 

 and thus throws the articulation of the lower jaw far back, giving rise to a very 

 wide gape. In most Snakes, and particularly in the Viperine forms, the facial 

 pable of movement upon one another, but in Typhlops they are im- 



FIG. 75. SKULL OF A YOUNG 

 CROCODILE. (Ventral view.) 



Cocc, occipital condyles ; Ob, 

 basioccipital ; Ch, internal 

 nostrils ; Pt, pterygoid ; Orb, 

 orbit ; PI, palatine ; M, 

 palatine process of maxilla ; 

 Pmx, premaxilla ; Ts, trans- 

 verse bone ; Jy, jugal ; Qj, 

 quadratojugal ( ' ' paraquad- 

 rate," Gaupp) ; Qu, quadrate. 



bones are ca 



movably connected with the skulL 



by a more or less elastic ligament. 



The two rami of the mandible are connected 



